Synchrotron X-ray scattering studies at mineral-water interfaces

Synchrotron X-ray scattering techniques provide a powerful tool for the in situ study of atomic scale processes occurring at solid-liquid interfaces. We have applied these techniques to characterize and study reactions at mineral-water interfaces. Here we present two examples. The first is the characterization of the calcite (CaCO{sub 3}) (10{bar 1}4) cleavage surface, in equilibrium with deionized water, by crystal truncation rod measurements. The second is the in situ study of the heteroepitaxial growth of otavite (CdCO{sub 3}) on the calcite (10{bar 1}4) cleavage surface. The results of such studies will lead to significant progress in understanding mineral-water interface geochemistry

Stable isotopic investigations of in situ bioremediation of chlorinated organic solvents. 1997 annual progress report

'The author has made significant progress in developing innovative methods for investigating the mechanism and extent of in situ bioremediation of chlorinated organic solvents. These methods use precise isotopic ratio measurements of chlorine and carbon in reactant and product species in laboratory experiments and in materials from field demonstration sites. Specific tasks completed during FY 1997 include: (1) refinement and publication of a new analytical method for precise determination of chlorine and carbon isotope ratios in chlorinated volatile organic compounds; (2) laboratory experiments involving biological degradation of chlorinated solvents in liquid cultures and soil columns; and (3) use of chlorine and carbon isotope ratios to investigate natural attenuation of trichloroethene at the Paducah Gaseous Diffusion Plant. This work can have immediate impact because it will provide the fundamental basis for a new and cost-effective means of evaluating and monitoring the effectiveness of in situ bioremediation schemes for chlorinated organic solvents in soils, vadose horizons, and groundwater plumes.

Stable isotopic investigations of in-situ bioremediation of chlorinated organic solvents

The purpose of this project was to investigate the potential applications of stable isotope ratio measurements in characterization of the source terms, the transport, and the fate of chlorinated solvents in groundwater aquifers. The approach to this research was threefold: to develop methods for the sampling and isotopic analysis of chlorinated solvents in groundwaters; to perform laboratory experiments to measure equilibrium and kinetic isotope effects associated with biological and physical transformation processes of chlorinated solvents; and to perform field investigations at well-characterized, contaminated aquifer sites to demonstrate the applicability of the isotopic approach in real-world situations. New methods were developed for the extraction and isotopic analysis of chlorinated solvents in water samples. The new methods were applied to a series of laboratory experiments assessing the isotope effects associated with biological and physical transformation processes. The authors found that a large kinetic isotope effect was caused by microbial degradation of chlorinated solvents, under both aerobic and anaerobic conditions. The evaporation of chlorinated solvents also caused a large isotope effect, but in that case the carbon isotopic fractionation was in the reverse sense. Isotopic fractionation associated with adsorption and chemical exchange of chlorinated solvents was negligible. The authors performed field investigations at five present and former industrial sites undergoing various stages of remediation. These investigations were collaborative with Lockeed-Martin Energy Systems, Inc., and ENSR, Inc., the companies responsible for the remedial work at these sites. Application of the new sampling and analytical methods at these sites showed that stable isotopic measurements yield powerful insights into underground processes. In particular, they found positive evidence for in-situ microbial degradation of chlorinated solvents at all five sites, evidence for volatilization of chlorinated solvents at three sites, and evidence for multiple sources of chlorinated solvents at two sites. At a site where six-phase heating was applied, they found evidence for increased solubilization of pure phase chlorinated solvents during heating. The general conclusion of the field investigations is that stable isotope measurements should become an essential component in site characterization and remediation of sites contaminated with chlorinated solvents

Stable isotopic investigations of in-situ bioremediation of chlorinated organic solvents. 1998 annual progress report

'Contamination of soils and groundwaters with chlorinated aliphatic hydrocarbons (CAHs) is one of the most serious environmental problems in the DOE system and in the nation at large. These compounds are designated as priority pollutants by the US Environmental Protection Agency (EPA) and are known or suspected to be carcinogenic or mutagenic in humans. These compounds are readily transported by groundwater and are not reduced to acceptable concentrations for human consumption by most municipal water supply treatments; thus the compounds represent a significant hazard to a large portion of the human population. In situ bioremediation is an emerging technology that shows great promise for mitigation of CAH contamination at many sites. One of the most severe limitations of in-situ bioremediation is the difficulty of proving when it is working at a given site. The concentrations of CAHs and their degradation products in plumes may be difficult to relate to the efficiency of the remediation process because of dilution effects, but this problem is mitigated to a large extent by measuring isotope ratios. If there is a significant isotopic fractionation between CAHs and derivative chlorine-bearing products, then the fraction of CAH that is dechlorinated can be inferred from the {sup 37}Cl/{sup 35}Cl and {sup 13}C/{sup 12}C isotope ratios of the residual CAH. It is important to point out that there is currently no published information available on the magnitude of chlorine and carbon isotopic fractionation associated with biological degradation of CAHs. The authors plan to help eliminate this important gap in the knowledge with the work being performed here. This work is relevant to EMSP goals because it will provide a new and cost-effective means of evaluating and monitoring the effectiveness of in-situ bioremediation. It will employ newly developed techniques to characterize isotopic fractionation (of chlorine and carbon) associated with biotic and abiotic degradation of CAHs in laboratory microcosms. These techniques and the data acquired by using them in laboratory studies will form the fundamental basis for quantitative assessment of the mechanisms, rates, and efficiencies of various in-situ bioremediation schemes for CAHs. This report summarizes work as of 21 months into a 36-month project. First, the author has developed methods for precise measurement of stable carbon and chlorine isotope ratios of micromolar amounts of CAHs. He has also developed methods for quantitative extraction of CAHs from water and air. He has applied these methods in laboratory experiments, to investigate isotopic fractionation caused by microbial degradation and by abiotic processes such as evaporation and chemical reduction. He has also applied these methods to field investigations of contaminated groundwater aquifers at the Paducah Gaseous Diffusion Plant, Kentucky and at several manufacturing plants in the Chicago and Kansas City metropolitan areas. Results of much of this work have already been incorporated into four manuscripts that have been published, accepted for publication, or are in review.

Behavior of nuclear waste elements during hydrothermal alteration of glassy rhyolite in an active geothermal system: Yellowstone National Park, Wyoming

The behavior of a group of nuclear waste elements (U, Th, Sr, Zr, Sb, Cs, Ba, and Sm) during hydrothermal alteration of glassy rhyolite is investigated through detailed geochemical analyses of whole rocks, glass and mineral separates, and thermal waters. Significant mobility of U, Sr, Sb, Cs, and Ba is found, and the role of sorption processes in their observed behavior is identified. Th, Zr, and Sm are relatively immobile, except on a microscopic scale. 9 references, 2 figures, 2 tables

Dissolution dynamics of the calcite-water interface observed in situ by glancing-incidence X-ray scattering

Glancing-incidence X-ray scattering measurements made at the National Synchrotron Light Source were used to investigate dissolution dynamics in situ at the calcite-water interface. The relation between calcite saturation state and roughness of the calcite (1014) cleavage surface as a function of time was examined during pH titrations of an initially calcite-saturated solution. Systematic variations in roughness were observed as a function of saturation state as pH was titrated to values below that of calcite saturation. Different steady-state values of roughness were evident at fixed values of {Delta}G{sub r}, and these were correlated with the extent of undersaturation. A significant increase in roughness begins to occur with increasing undersaturation at a {Delta}G{sub r} value of approximately {minus}2.0 kcal/mol. The dissolution rate corresponding to this increase is about 1.5 x 10{sup 7} mmol/cm {center_dot} sec. This increase in roughness is attributed to a transition in the principal rate-determining dissolution mechanism, and is consistent with both powder-reaction studies of dissolution kinetics and single-crystal dissolution studies by atomic force microscopy. These data indicate some important potential applications of GIXS in the study of mineral-water interface geochemistry

U/Th geochronology of hydrothermal activity in Long Valley caldera: Little Hot Creek and the Blue Chert

To better define the evolution of the Long Valley hydrothermal system, we have embarked on a program of U/Th age determinations of hydrothermal products from outcrops and drill cores within the caldera. The U/Th system is appropriate for determining ages less than about 350 Ka in suitable materials. Results presented are from dense chalcedonic silica veins, collected from base to top of the outcrop beginning 40 m N of hot spring LHC-1 in Little Hot Creek canyon, and from samples of the Blue Chert

An atom counter for measuring 81Kr and 85Kr in environmental samples

Due to its simple production and transport processes in the terrestrial environment, the long-lived noble-gas isotope 81Kr is the ideal tracer for old water and ice in the age range of 10 5-10 6 years, a range beyond the reach of 14C. 81Kr-dating, a concept pursued in the past four decades by numerous laboratories employing a variety of techniques, is now available for the first time to the earth science community at large. This is made possible by the development of ATTA-3, an efficient and selective atom counter based on the Atom Trap Trace Analysis method and capable of measuring both 81Kr/Kr and 85Kr/Kr ratios of environmental samples in the range of 10 -14-10 -10. The instrument was calibrated with 12 samples whose 85Kr/Kr ratios were independently measured using Low Level Decay Counting, including six samples that were measured in a blind arrangement. Compared to the previously reported ATTA-2 instrument, the counting rates of ATTA-3 are higher by two orders of magnitude and the required sample size lower by one order of magnitude. For 81Kr-dating in the age range of 150-1500kyr, the required sample size is 5-10μL STP of krypton gas, which can be extracted from approximately 100-200kg of water or 40-80kg of ice. Moreover, a laser-induced quenching scheme was developed to enable measurements of both the rare 81,85Kr and the abundant 83Kr, whose isotopic abundances differ by 11 orders of magnitude. This scheme allows ATTA-3 to directly determine 81Kr/Kr and 85Kr/Kr ratios without other supplemental measurements. Combining the significant reduction in sample size with numerous advances in the measurement procedure, ATTA-3 represents the state-of-the-art instrument for routine analysis of these rare noble gas tracers in a wide range of earth science applications. © 2012 Elsevier Ltd